Conventional methods for drycleaning use a chlorinated hydrocarbon solvent, most commonly perchloroethylene (PERC) in combination with small amounts of water and detergents. Although PERC is fabric-safe, non-flammable, and easily recycled, it poses environmental risks and health hazards. In particular, PERC has toxicological issues associated with its use, the EPA lists it as a Hazardous Air Pollutant (HAP), and it is non-biodegradable.
In response to the safety and health risks of PERC, the industry has commercialized less-toxic alternatives. For example, GreenEarth Cleaning, produces a cyclic siloxane, which is optionally combined with a glycol ether or another organic solvent (see, e.g., U.S. Pat. Nos. 6,042,617 and 6,063,135). Another common alternative is hydrocarbons. Hydrocarbons used in the drycleaning industry are typically blends of C10 to C15 aliphatic compounds. Examples include DF-2000 fluid (a product of ExxonMobil Chemical) and EcoSolv® drycleaning fluid (a product of Chevron Phillips Chemical).
Glycol ethers, which offer good cleaning properties for both oil-soluble and water-soluble stains, are another attractive alternative. Notable glycol ethers include propylene glycol tert-butyl ether, propylene glycol n-butyl ether, dipropylene glycol tert-butyl ether (DPtB), and dipropylene glycol n-butyl ether (DPnB) as taught in U.S. Pat. Nos. 5,888,250 or 6,273,919. Mixtures of dipropylene glycol n-propyl ether (DPnP) and water (U.S. Pat. No. 7,087,094) or dipropylene glycol dimethyl ether (DMM) and water (U.S. Pat. Appl. Pub. No. 2006/0042021) have also been taught. Other mixtures containing DPnP or DMM and water or other solvents are described in WO 01/16422 (DPnP combined with less than 1 wt. % of water) and U.S. Pat. No. 6,828,292 (85 wt. % of DMM combined with 10 wt. % of water). U.S. Pat. No. 6,755,871 teaches a pressurized cleaning system containing one or more organic solvents including glycol ethers and aliphatic hydrocarbons. U.S. Pat. No. 6,086,634 teaches a drycleaning composition comprising glycol ethers, water, and polysulfonic acid. None of the above-mentioned references describes particular mixtures of dipropylene glycol C3-C4 alkyl ethers, water, and C10-C15 aliphatic hydrocarbon mixtures.
Drycleaners using glycol ether cleaners occasionally report odors from residual solvent in drycleaned fabrics or garments. Consumers more accustomed to the odor of residual PERC also notice it. Not surprisingly, the odor is most noticeable in heavy fabrics, multilayer textiles, and garments with structural components such as shoulder pads. While the odor can be reduced by increasing the temperature or drying time, either approach increases the cost of an already energy-intensive operation and slows the production rate. Another possible approach would be to combine a higher boiling glycol ether with a more-volatile solvent to enhance evaporation. However, this approach would do little to remove the last traces of the higher-boiling glycol ether.
Although progress in finding replacements for PERC has been made, consumer acceptance is key to adoption of safer alternatives. An ideal drycleaning method would clean both oil and water-based stains, with a minimum of fabric shrinkage. In addition, the method would promote fast evaporation and allow for complete or near-complete removal of solvent so that the drycleaned article is essentially odorless. Ideally, this could be done without increasing the temperature and time at which garments are drycleaned.